The proposed work continues investigation of the regulation of a group of inducible functions (SOS functions) which are coordinately expressed in response to DNA damage by many mutagenic and carcinogenic agents in bacteria. One of the functions expressed is an error-prone repair activity that is responsible for ultraviolet-light-induced mutagenesis, and for mutagenesis by many other agents. Mutations in many genes affect the expression of these functions differentially. Mutations that suppress filamentous growth (Sfi mutations) appear to influence the induction and/or expression of SOS functions via changes in activity and specificity of proteolytic enzymes. We continue to map genes in which Sfi mutations occur, to analyze their effects (singly and in combinations) on the expression of SOS functions, and to determine whether their primary effects are on the composition of the outer membrane. Our working hypothesis is that altered outer membrane structure affects the activity and the specificity of one or more membrane-associated proteases, and that Sfi mutations "fine-tune" SOS functions by altering outer membrane proteins. The use of gel electrophoresis, to identify outer membrane proteins in Sfi mutants and their strains, will supplement genetic analysis.